When an oil or gas well is drilled and the casing is in place, the casing is pierced so the oil or gas can flow into the casing and the well can start producing. A "Christmas tree" is installed at the top of the hole and includes piping and valves. It is made to withstand the high pressures that may be exerted by gases and fluids in the hole.
In order to go back into the hole through the Christmas tree to install tubing once the well is under pressure, it is necessary to use some type of method for balancing that pressure to prevent a blowout. Usually, fluids such as water or denser fluids are used to balance the pressure. This is very expensive, and the use of any fluid tends to damage the geological formation. An alternative which does not require fluid is to use a snubbing unit which is known in the art. The snubbing unit uses rams or seals to seal off tubing strings when moving pipe into or out of a well under pressure.
When oil well tubing is located in an area in which streams of fluid carrying sand impinge on the tubing, holes can quickly be cut in the tubing by the sand-blasting effect. Blast joints have been used in the past to protect the tubing from such sand-blasting action. Blast joints are usually a series of carbide rings stacked up on top of each other to surround the tubing and protect it from the cutting action described above.
Because these blast joints can be fairly long, and because the rings do not provide a pressure seal, these blast joints do not lend themselves to being inserted through a snubbing unit.
Thus, until the present invention, there was no effective way to protect tubing from the cutting action of streams of sand if the tubing was installed through a snubbing unit. Either the tubing would have to be inserted through the snubbing unit unprotected, or a fluid would have to be used to balance the pressure so that a standard blast joint could be used. The substantial opportunity for the fluid to damage the formation and the cost of the fluid itself are factors that often make the second alternative undesirable, and, of course, it is not acceptable to install the tubing unprotected into an area in which it will rapidly be cut by streams of sand.